Multifunctional Four-Port MIMO Antenna for Sub-6 GHz Applications

A switchable four port multiple input multiple output (MIMO) antenna has been presented in this paper for sub-6 GHz underlay cognitive radio applications. The proposed antenna is made on a coplanar waveguide (CPW) concept with a microstrip line feeding a semicircular patch element. Two narrow width slots are etched in the feed line, and one p-i-n diode is carefully placed across the pathway such that the overall geometry exhibits a switching response between an ultra-wideband (UWB) and a bandstop response. During the UWB state, the single antenna exhibits a wide impedance bandwidth (reflection coefficient <-10 dB) from 2.7 GHz to 6.30 GHz, thereby behaving as a sensing antenna. On the contrary, a bandstop response is obtained from 3.3 GHz to 4.3 GHz during the reverse bias of the diode. Afterward, a four-port MIMO antenna has been designed, where satisfactorily values are attained for various critical antenna parameters, such as isolation between antenna elements (<20 dB), envelope correlation coefficient (<0.5), and channel capacity loss (<0.5 bits/sec/Hz). Low profile, compact size, and ease of switching between the states make the proposed antenna geometry suitable for various wireless communications.